This invention relates to the field of pressure sensitive labels.
In a typical process for manufacturing pressure sensitive adhesive labels, a solution of a pressure sensitive material is continuously and uniformly applied to the reverse side of a substrate, or face stock, usually paper, in the form of a continuous web and dried. Thereafter a release sheet usually provided as a continuous paper web coated with a release agent, is applied to the exposed pressure sensitive adhesive surface to form a substrate-pressure sensitive adhesive-release sheet label stock which is then wound on a rewind roll for further processing such as sheeting, slitting or other converting. After that, the label stock is typically printed, cut and collated by a printer to form individual printed sheets. Such sheets may be utilized for any number of uses including name tags, stickers, labels, etc., by simply peeling away the release paper and pressing the adhesive-coated side of the face sheet to the desired surface.
U.S. Pat. No. 4,587,158 describes a polyethylene-based label for application to collapsible wall type containers, e.g., squeeze bottles, for dispensing a variety of liquids and solids. The label is said to have the ability to adhere to flexible surfaces throughout severe mechanical stress, temperature change or atmospheric exposure without shrinking, loosening, scratching or otherwise defacing. The label is corona treated or otherwise modified to render the surface more suitable for printing and for essentially permanent bonding employing pressure separative adhesives characterized by their ability to cure to permanent set while maintaining an elastic nature, e.g., copolymers of acrylic esters such as 2-ethylhexyl acrylate with polar co-monomers such as acrylic acid. From examples illustrating the manufacture of such a label, it is clear that the pressure sensitive adhesive is intended to be applied more or less uniformly to an entire surface thereof.
U.S. Pat. No. 4,377,616, the contents of which are incorporated by reference herein, discloses a lustrous, opaque biaxially oriented polymer laminate film structure comprising a thermoplastic polymer matrix core layer possessing numerous voids, a substantial number of which contain at least one void-initiating particle, and transparent skin layers adhering to the surfaces of the core layer. The unique structure of the core layer imparts a much higher degree of opacity, possibly due to the effects of light scattering, than that possible by the use of opacifying pigment alone.
U.S. Pat. Nos. 4,582,736 and 4,626,460, the contents of which are also incorporated by reference herein, each describes a coextruded pressure sensitive label stock material possessing an integral peelable backing and a facing component based on the lustrous, opaque laminate film of U.S. Pat. No. 4,377,616.
It has been observed that when a label facing based on the lustrous, opaque laminate film of U.S. Pat. No. 4,377,616 which possesses a substantially continuous, uniformly applied layer of pressure sensitive adhesive on its reverse side is applied to a collapsible wall type container, e.g., a squeeze bottle or flexible tube container, there is a pronounced tendency for the label to form permanent unsightly creases, or wrinkles, when the container is compressed to dispense product therefrom. Repeated use of such a container will often result in a large number of creases the overall appearance of which can be likened to shattered glass.
While the reason for this phenomenon is not known with certainty, studies of the problem appear to indicate that compression of the bottle to dispense its contents results in differential movement of the outermost layer of the laminate facing relative to the innermost layer which tends to remain anchored in place on the container wall by the pressure sensitive adhesive. This differential movement is believed to result from the separating and tearing away of the outermost layer from the innermost layer, the aforementioned wrinkled appearance of the label being the visual result of this structural deformation in the label facing.
Whatever may be the actual explanation for the foregoing wrinkling phenomenon, the fact remains that such wrinkling constitutes a significant drawback to the use of the lustrous, opaque laminate film of U.S. Pat. No. 4,377,616 as a pressure sensitive label facing for application to collapsible wall type containers.